This invention relates to a high volume covered hopper car, such as typically used to transport granular or pulverant ladings, such as flour, cement, plastic pellets or powders, and the like.
Generally, covered hopper cars, such as are shown in the co-assigned U.S. Pat. No. 3,339,499 and 3,490,387, have come into widespread service. These covered hopper cars give many advantages to shipping granular or pulverant materials, facilitate loading and unloading of the lading, and maintain the lading in a clean, controlled environment during loading, transport, storage within the car, and during unloading. In the shipping of various granular or pulverant ladings, it is desirable that the car carry the maximum amount of the lading. Certain particulate ladings have bulk densities such that the lading carrying capability of a covered hopper car is limited by its lading volume capability rather than by the weight of the lading. Thus, there has been a long-standing need in the design of covered hopper cars to achieve as high a lading carrying volume as possible.
All railroad cars must fit within a three-dimensional clearance envelope, as defined by the Association of American Railroads (AAR). Generally, this AAR clearance envelope defines the maximum height, width, and length of a car such that the car will be able to negotiate railroad tracks across the country, and be able to pass through tunnels, over bridges, around curves, and past other trackside objects without interference. These clearance standards are specified in the AAR's "Specifications For Design, Fabrication, And Construction Of Freight Cars", which is in part set out in ACF Industries' Shippers' Car Line Division Service Bulletin 12a, entitled "Plate B and Plate C Clearance Diagrams", issued October, 1967, a copy of which is included in the file of the present specification, and is herein incorporated by reference.
Generally, two clearance diagrams or envelopes, known as AAR Plate B and Plate C are utilized. These clearance diagrams are actually composites of the clearance diagrams for all of the railroads in the country and may be considered to be a three-dimensional "tunnel" through which a car must be able to pass without touching the "tunnel". Not only must the car be able to pass through the "tunnel", but all car appurtenances, such as walkways, ladders, hatches, railings, etc., must also be kept within the limits of the diagrams. The AAR has defined a "base" car for both Plate B and Plate C clearances. In general terms, Plate B cars have a somewhat lower height (15 feet, 1 inch) than Plate C cars (15 feet, 6 inches), and may operate in unrestricted interchange service. Since Plate C cars are somewhat taller, these cars may operate in limited or restricted interchange service, and may be permitted only on certain routes. However, the restrictions placed on Plate C cars are relatively few in number, and for purposes of this disclosure, Plate C will be utilized as the standard clearance envelope for the railroad car of the present invention.
A freight car must not only be sufficiently narrow and less than a maximum predetermined height to pass through the AAR Plate C clearance diagram, but the maximum allowable width of the car is dependent on the distance between the centerlines of the trucks at the opposite ends of the car, and also on the amount of overhang or swing-out at the ends of the car. As will be appreciated, as a railroad car negotiates a curve, the center section of the car will move radially inwardly and the ends of the cars will move radially outwardly relative to a chord defined by the centerlines of the trucks of the car. The maximum curve considered by the AAR clearance diagrams is a 13 degree curve, having a radius of 441 feet, 8.375 inches. The AAR Plate C base car, having truck centers less than 46 feet, 3 inches, may have a maximum width of 10 feet, 8 inches. However, a car having truck centers spaced at the maximum permitted distance between truck centers of 81 feet may only be 8 feet, 2 inches wide. Cars of an intermediate length may have a maximum width between these two extremes, with the maximum width being dependent on the length of the car, as defined by the above-noted AAR specifications.
Thus, for one of ordinary skill in the art designing a covered hopper car maximizing the lading volume of the car, and optimizing the use of the materials utilized to construct the car, it is not practical to increase the lading volume of the car merely by increasing its length.
As is well known, the structure of center stub sill railroad cars requires that the upper chords of the car carry both certain bending loads applied to the car by the weight of the lading and the car, and certain train loads. These train loads typically take the form of forces required to resist moments induced in the end structure of the car due to the vertical offset between the centerline of the coupler and the respective cross section of the car. It has been found that center stub sill cars having smooth side sheets have a tendency to induce buckling in the areas of attachment of the side sheets to the side sills, and in the areas of attachment of the side sheets to the top chord or side plate reinforcement members. This tendency of the side sheets to buckle is sometimes referred to as diagonal buckling, which is caused by diagonal tension field effects, and which is most pronounced at the upper and lower ends of the side sheets. To further aid in understanding this buckling problem, the side sills, the top chord or side members, and the side sheets form a composite beam structure, with the side sheets constituting the web of the beam structure, and with the side sill and the top chord members constituting the upper and lower flanges or chords of the beam structure. However, since the thickness of the side sheet is relatively thin (typically the side sheets are approximately 3/16 inch [4.7 mm.] or less in thickness), and since the height of the side sheets is great (e.g., 10 or more feet [3 m.]), the side sheets are not inherently stable, and their resistance to buckling under loading is relatively low.
As noted above, the side sheets must have sufficient resistance to buckling and to other structural failure, with an adequate margin of safety under all anticipated normal operating conditions for the car. If straight, vertical side sheets are utilized, it has been found necessary to provide vertical stringers or hat sections at spaced intervals along the length of the side sheets to reinforce the side sheets against buckling. If these vertical hat sections are secured to the inside face of the side sheets, no appreciable lading volume is taken up within the car, but the lading will tend to accumulate in these hat sections and at the intersections of the various components of the car and the hat sections, thus making the lading difficult to clean from the car. A car which is difficult to clean may contaminate the next lading carried by the car. If the hat sections are placed on the outside of the car, the side sheets must be moved inwardly at least the depth of the hat sections, and thus the maximum lading volume of the car is appreciably decreased.
As described in the aforementioned co-assigned U.S. Pat. No. 3,490,387, the side sheets of prior art cars are generally of an arcuate shape struck from a generally constant radius, having a center at a substantial distance outside the confines of the car. More specifically, the radius of curvature of the arcuate side sheets of the prior art covered hopper cars disclosed in U.S. Pat. No. 3,490,387 was specified to have a radius of curvature between about 160-195 inches (see column 2, lines 30-35, of U.S. Pat. No. 3,490,387). Generally, these prior art covered hopper cars, in end elevation view, had a part cylindrical car body, with the radius of the sidewalls being substantially larger than the width of the car. It will thus be appreciated that if the cross section of the body of such prior art covered hopper cars were placed within the confines of the AAR Plate C height and width template, the bottom and tops of the side walls would be spaced a considerable distance from the confines of the AAR Plate C clearance diagram, as shown in FIG. 4. However, it has been found that if a substantially larger radius of curvature is utilized so as to increase the volume of the hopper car and yet still remain within the confines of the AAR Plate C diagram, the relatively thin side sheets will not have adequate resistance to diagonal buckling along their lower portions proximate the side sills, and along their upper portions proximate the cover sheets
Thus, there has been a long-standing need for a covered hopper car having thin-walled side sheets without penalizing vertical reinforcements, and having adequate resistance to buckling.